Yoon H S, Golden J W
Department of Biology, Texas A&M University, College Station, Texas 77843-3258, USA.
J Bacteriol. 2001 Apr;183(8):2605-13. doi: 10.1128/JB.183.8.2605-2613.2001.
The filamentous cyanobacterium Anabaena sp. strain PCC 7120 forms a developmental pattern of single heterocysts separated by approximately 10 vegetative cells. Heterocysts differentiate from vegetative cells and are specialized for nitrogen fixation. The patS gene, which encodes a small peptide that inhibits heterocyst differentiation, is expressed in proheterocysts and plays a critical role in establishing the heterocyst pattern. Here we present further analysis of patS expression and heterocyst pattern formation. A patS-gfp reporter strain revealed clusters of patS-expressing cells during the early stage of heterocyst differentiation. PatS signaling is likely to be involved in the resolution of these clusters. Differentiating cells were inhibited by PatS during the time period 6 to 12 h after heterocyst induction, when groups of differentiating cells were being resolved to a single proheterocyst. Increased transcription of patS during development coincided with expression from a new transcription start site. In vegetative cells grown on nitrate, the 5' end of a transcript for patS was localized 314 bases upstream from the first translation initiation codon. After heterocyst induction, a new transcript with a 5' end at -39 bases replaced the vegetative cell transcript. A patS mutant grown for several days under nitrogen-fixing conditions showed partial restoration of the normal heterocyst pattern, presumably because of a gradient of nitrogen compounds supplied by the heterocysts. The patS mutant formed heterocysts when grown in the presence of nitrate but showed no nitrogenase activity and no obvious heterocyst pattern. We conclude that PatS and products of nitrogen fixation are the main signals determining the heterocyst pattern.
丝状蓝细菌鱼腥藻Anabaena sp. PCC 7120菌株形成一种发育模式，即单个异形胞被大约10个营养细胞隔开。异形胞由营养细胞分化而来，专门用于固氮。patS基因编码一种抑制异形胞分化的小肽，在原异形胞中表达，在建立异形胞模式中起关键作用。在此，我们对patS表达和异形胞模式形成进行了进一步分析。一个patS-gfp报告菌株在异形胞分化早期显示出patS表达细胞簇。PatS信号可能参与了这些细胞簇的解体。在异形胞诱导后6至12小时期间，当分化细胞群正在解聚为单个原异形胞时，分化细胞受到PatS的抑制。发育过程中patS转录增加与一个新转录起始位点的表达同时发生。在以硝酸盐为生长底物的营养细胞中，patS转录本的5'端位于第一个翻译起始密码子上游314个碱基处。异形胞诱导后，一个5'端位于-39碱基处的新转录本取代了营养细胞转录本。在固氮条件下生长数天的patS突变体显示出正常异形胞模式的部分恢复，推测是由于异形胞提供的氮化合物梯度所致。patS突变体在硝酸盐存在下生长时形成异形胞，但没有固氮酶活性，也没有明显的异形胞模式。我们得出结论，PatS和固氮产物是决定异形胞模式的主要信号。
